The Roux-en-Y gastric bypass operation combines restrictive and malabsorptive principles. It is the most commonly performed bariatric procedure worldwide (~ 50 %). Vertical (sleeve) gastrectomy on the other hand, is a purely restrictive procedure and has gained popularity and is now accepted as a valid procedure accounting for approximately five percent of the bariatric procedures performed worldwide.

The remission rate of type 2 diabetes one to two years after bariatric surgery is approximately 70%. Some studies have indicate that the remission rate of type 2 diabetes is higher after gastric bypass than after sleeve gastrectomy. Other studies indicate a similar effect on the reduction in HbA1c.

Weight reduction is comparable between gastric bypass and sleeve gastrectomy although some evidence suggets a larger weight loss following gastric bypass surgery. Larger weight loss can clearly contribute to somewhat greater improvement in glucose homeostasis after gastric bypass than after sleeve gastrectomy. Still, one might speculate that changes in gut hormones may contribute to higher remission rates of type 2 diabetes after gastric bypass than after sleeve gastrectomy.

Improved β-cell function observed after gastric bypass surgery may be linked to higher postprandial levels of Glucagonlike peptide 1 as seen after gastric bypass surgery. Beta cell function has, to our knowledge, only been addressed in one previous study after sleeve gastrectomy, with the authors reporting an increased first-phase insulin secretion three days after the procedure. Although several studies have addressed changes in gastrointestinal hormones the incretin effect on insulin secretion after gastric bypass has been estimated in only a few studies. To the best of our knowledge the incretin effect on insulin secretion after sleeve gastrectomy remains unexplored.We are aware of four ongoing randomised controlled trials comparing the effect of gastric bypass and sleeve gastrectomy on several endpoints including weight and comorbidities (ClinicalTrial.gov identifiers: NCT00722995, NCT00356213, NCT00793143, and NCT00667706). However, these studies include both subjects with and with-out type 2 diabetes and are therefore not powered to detect between-group differences in HbA1c and beta-cell function in the diabetic patients.

In conclusion, the effect of gastric bypass and sleeve gastrectomy on glycaemia is not fully elucidated. Moreover, the impact of altered beta-cell function post surgery needs to be explored. We hypothesise that greater improvement in beta-cell function after gastric bypass than after sleeve gastrectomy translates into better glycaemic control in subjects with type 2 diabetes one year after surgery.

Regular use (a total of 3 months cumulative use in the last 12 months) or treatment the past two months with oral or inhalation corticosteroids

Medication suspected to influence insulin secretion and action such as unselective β-blockers

Not able to give informed consent

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01778738